The present invention relates generally to light sources. More particularly, the present invention relates to light emitting semi-conductor light sources. The present invention has particular relevance to illumination of a display via a semiconductor device(s).
Conventional incandescent light bulbs have limited light efficiency. Conventional fluorescent light bulbs include mercury. Accordingly, there is a need for a light source that has long life and high efficiency and does not create environmental concerns.
One solution to this need is envisioned to be semi-conductor based light emitting diodes and laser diodes, herein after both are generally referred to as LED(s) The LED has a small size, high efficiency, can emit bright color light, and as a semiconductor element, is not vulnerable to breakage. Also, it has excellent initial driving characteristics and vibration resistance. Furthermore, it can withstand repeated ON/OFF cycling. Consequently, LEDs have been widely used as various types of indicators and light sources.
Recently, light emitting diodes of red, green and blue colors with high luminance and high efficiency have been developed, and these light emitting diodes have been used in manufacturing large size LED displays. In order to use light emitting diodes to get white light, since LEDs have monochromatic peak wavelengths, three LEDs of red, green and blue have been used in combination to diffuse and blend their colors into white. Such LED displays can operate at low power, have lite weight, and long life.
In addition, recently, efforts have been made to create individual light emitting diodes which emit white light. More particularly, a device that uses a fluorophor to convert non-white light emitted from the LED to white light has been used. Similarly, the use of a phosphor to create green, red and other colors is possible and can have particularly desirable use in display applications. Accordingly, recent technology has provided a wide spectrum of LED generated light colors suited to display applications. For example, a vehicle dashboard with multiple color LED generated presentations can be envisioned.
The suitable LED is typically constructed of a semiconductor epistructure light emitting element set in a cup on the tip of a lead frame. The light from the light emitting element is either already in a suitable/visible color (e.g. red) or is absorbed by a phosphor contained in a resin molding that covers the light emitting element. The phosphor emits at a wavelength different from the absorbed light (wavelength conversion) In one exemplary device, the light emitting element emits blue light and the phosphor absorbs the emitted blue light and emits yellow light The combination of yellow phosphor light and blue light emitting element light makes it is possible to manufacture an LED that can emit white light.
Generally, however, LED light is directional and does not evenly illuminate areas without diffusers or other light averaging structures with considerable light loss. Moreover, traditional LED structures produce illumination having an intensity pattern, as each LED device shines on a small area and may produce a halo effect via a high intensity spot at the center. This is not visually desirable nor aesthetically pleasing to the eye. Furthermore, these undesirable light patterns can light unnecessary areas and detract from the eye's ability to focus rapidly on a display. More particularly, since it is desirable to illuminate only certain numbers, messages, dials, etc. general lighting of the are is unacceptable. Similarly, general lighting on a surface can be problematic since the display targets (e.g. number, words, dials) may have surfaces with varied pitch which general lighting cannot readily illuminate.
This type of light distribution can be particularly troublesome when used to illuminate display surfaces, such as dashboards or control devices such as turning indicators. Moreover, areas of high and low light intensity are undesirable.
Furthermore, the addition of phosphors to an LED device results in a relatively costly manufacturing process that yields an apparatus which may lack consistency, maintainable color temperature and lumen integrity. Accordingly, current LED use in association with display surfaces could be improved.